U.S. Pat. No. 6,073,491 discloses an arrangement and a method for the contactless distance and pressure measurement within an air spring. Both measurement quantities are determined in accordance with the pulse/echo method with the aid of ultrasonic pulses, which propagate within the air spring flexible member. The distance between the ultrasonic transducer and an end reflector is computed from the running times of the sonic pulses to a first reference reflector and to the end reflector. The static pressure present in the air spring is determined with the aid of a second reference reflector at a defined distance to the first reference reflector. For this purpose, a control unit holds the amplitude of the first echo constant. The damping constant of the air and therefore the pressure is computed from the ratio of the amplitudes of the first and second reference echos.
From theoretical considerations, it results that this pressure-measurement method is not especially sensitive and therefore is rather imprecise. A further disadvantage is the relatively high technical complexity, namely, two reference reflectors and a control unit for the transmitting power are necessary.